The present invention relates to a method for producing a thermoelectric component comprising at least one pair of thermoelectric legs, including an n-leg and a p-leg, both legs being welded to an electrically conductive contact material. Furthermore, the present invention relates to a thermoelectric component.
The mode of operation of a thermoelectric component is based on the thermoelectric effect, which is also called Seebeck effect and Peltier effect, respectively. The field of application of the present invention is thus thermoelectrics. A thermoelectric component can be used on the one hand for generating energy as a thermoelectric generator and on the other hand for temperature control as a Peltier element. A third field of application for thermoelectric components are sensors—for example, thermoelements and thermocolumns.
In a thermoelectric generator, voltage and thus electric current is generated by way of a temperature difference. Inversely, in a Peltier element, one side of the thermoelectric component is heated by applying voltage and due to the resulting flow of current, and the other side of the thermoelectric component is cooled. When the thermoelectric component is used as a temperature sensor, a change in temperature is detected via a change in voltage at the output of the thermoelectric component.
FIG. 1 shows the basic structure of a thermoelectric component 1. In principle, such a thermoelectric component 1 is composed of pairs of thermoelectric legs with n-legs 2 and p-legs 3. These n- and p-legs 2, 3 are n- and p-conducting materials, as are also used in other fields of semiconductor technology. Due to an electrically conductive contact material 4 the n-legs 2 and the p-legs 3 are alternatingly contacted with one another. Thus the n- and p-legs 2, 3 are connected electrically in series and thermally in parallel. The pair of thermoelectric legs and the electrically conductive contact material 4 are provided between layers of an electrically insulating substrate 5.
As is schematically shown in FIG. 1, there is a temperature gradient from “hot” to cold” between an upper side of the thermoelectric component 1 and a lower side of the thermoelectric component 1. Due to this temperature gradient it is possible to use the thermoelectric component 1 as a thermoelectric generator so that voltage is applied between the outputs of the thermoelectric component. This is illustrated by the “minus” and the “plus” sign in FIG. 1
However, it is equally possible, with the same structure in FIG. 1, to generate a temperature gradient between the upper side and the lower side of the thermoelectric component 1 by applying an external voltage and with the current flowing in the circuit through the thermoelectric component. The thermoelectric component 1 is thus used as a Peltier element.
To contact the pairs of thermoelectric legs with the electrically conductive contact material 4, soldering methods or mechanical methods may be employed, for example.
In the soldering process a soldering paste or a liquid solder is normally applied in a screen-printing method. Alternatively, a solder can be applied by way of foil-shaped parts. Further solder coatings are formed by means of vaporization, sputtering, plasma spraying or electroplating methods.
Contacting by means of soldering methods has the drawback that the softening point of the solder must be higher than the operating temperature of the thermoelectric component. If the softening point of the solder is below the operating temperature of the thermoelectric component, the field of application of the thermoelectric component is restricted because at elevated temperatures the contact connections may fuse and the component may thereby get destroyed. Solders for thermoelectric applications in the range between 300° C. and 450° C. are not available.
Moreover, at operating temperatures above 250° C. the solders that can be used for thermoelectric components show further defects such as brittleness. As a rule, an additional electrical and thermal resistance that further reduces the efficiency of the thermoelectric component is inevitably created by the solder layer.
In mechanical bonding methods, e.g. sintering electrically conductive braiding into thermoelectric material or pressing electrical contacts against the thermoelectric material, the complicated manufacture of the thermoelectric components is disadvantageous. Moreover, mechanically pressed contacts show poor electrical and thermal properties, whereby the efficiency of such thermoelectric components is reduced.